A known method of teaching an industrial robot part such as an arm to transverse a path uses a control unit for successively storing points indicative of the moving part path. The points are derived at predetermined travelling distance intervals or at predetermined time intervals. In playback, the control unit controls the moving part in accordance with the stored points to trace the path made by the moving part. However, since such a teaching method involves moving the moving part linearly between the stored points, the interval must be relatively short to provide the required tracing precision. This results in a large capacity memory requirement.
A known technique for eliminating such a large capacity memory problem is disclosed in Japanese Patent Provisional Publication No. 56-114685, that includes a control unit for storing a subsequent point Pn+1 when the moving robot part position is greater than a predetermined distance from an extension of a straight line between a presently stored point Pn and a previously stored point Pn-1. While successfully avoiding the above-noted problem for a movement path having many straight portions because the point is not stored when the moving part travels substantially along a straight line, this technique is not well adapted for a path having complex portions such as curved portion.
Another approach for eliminating the large capacity problem is disclosed in Japanese Patent Provisional Publication No. 58-176705 having a temporary memory for temporarily simultaneously storing a present point Pn and an angle between a first straight line that connects point Pn with a previously stored point Pn-1 and a second straight line that connects point Pn-1 and a stored point Pn-2 derived prior to point Pn-1. Initial point P1, present point Pn and an intermediate point therebetween are supplied as path data from the temporary memory to a main memory when the angle results in a predetermined condition. Although satisfactory for a path having many curved portions, this prior art technique is disadvantageous for a path that does not have complex portions because the temporary memory must store a large amount of data and thus must have a large capacity.